From 7ed7031466cd77e4568de9f5ab0cee9cc5afafb8 Mon Sep 17 00:00:00 2001
From: Steve Baker <sbaker@redhat.com>
Date: Thu, 24 Apr 2014 16:25:55 +1200
Subject: [PATCH] Fetch all db resources in one query

Instead of calling resource_get_by_name_and_stack once for every
resource in the stack, db_api.resource_get_all_by_stack is called
only once for all resources.

This reduces the number of sql queries during a describe_stack_resource
call to 3:
1. load the stack
2. load the template
3. load the resources

This is a big improvement over the start of this patch series, which
is 2 queries plus:
* 1 per resource in the stack
* 1 per access to a resource metadata attribute
* 1 per access to a resource data value

There is probably still potential to reduce queries from 3, but this
may well be a fix for
Partial-Bug: 1306743

Change-Id: I80be5d3de8744813d974f2e9860c148ad258f385
---
 heat/engine/parser.py | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/heat/engine/parser.py b/heat/engine/parser.py
index e076f75494..8c6d1a3651 100644
--- a/heat/engine/parser.py
+++ b/heat/engine/parser.py
@@ -88,6 +88,7 @@ class Stack(collections.Mapping):
         self._resources = None
         self._dependencies = None
         self._access_allowed_handlers = {}
+        self._db_resources = None
         self.adopt_stack_data = adopt_stack_data
         self.stack_user_project_id = stack_user_project_id
         self.created_time = created_time
@@ -119,13 +120,21 @@ class Stack(collections.Mapping):
             self._resources = dict((name, resource.Resource(name, data, self))
                                    for (name, data) in
                                    template_resources.items())
+            # There is no need to continue storing the db resources
+            # after resource creation
+            self._db_resources = None
         return self._resources
 
     def db_resource_get(self, name):
         if not self.id:
             return None
-        return db_api.resource_get_by_name_and_stack(self.context,
-                                                     name, self.id)
+        if self._db_resources is None:
+            try:
+                self._db_resources = db_api.resource_get_all_by_stack(
+                    self.context, self.id)
+            except exception.NotFound:
+                return None
+        return self._db_resources.get(name)
 
     @property
     def dependencies(self):